Processing natural language for numerous applications is generally well known. Recent interest in processing has been due in large part by computer applications such as language translation, grammatical correction of sentences as part of word processing systems, and the like. For example, Machine Translation Technology: On the Way to Market Introduction, Siemens Review, Vol. 54, No. 6 Nov/Dec (1987) describe research into machine translation of text in several languages. Also, the use of language parsing in processing natural language is well known. Many parsing techniques have been described, see for example, J. J. Robinson, Diagrams: A Grammar for Dialogues, Communication of the Association for Computing Machinery, Vol. 25, No. 1, Jan. 1982, pp. 27-47, which discloses an interactive filter procedure, a grammar core, a weakening factor, a probability factor and a threshold mechanism; and K. Vehara, et al., Steps Toward an Actor-Oriented Integrated Parser, Proceeding of the International Conference of Fifth Generation of Computer Systems 1984, Tokyo, Japan, Nov. 6-9, 1984 (ICOT, North Holland).
Methods of grammatically processing a sentence using parsers are described in: Allen, James; Natural Language Understanding. (The Benjamin/Cummings Publishing Company Inc., Menlo Park, U.S.A. 1987.)
The parsers there described operate according to an algorithm based on a rewriting mechanism. This mechanism requires that the parsers carry out parsing by reference to a large number of rewriting rules. These rewriting rules make a connection between a group of words and/or sentence constituents, on the one hand, and a parent constituent, i.e. a constituent dominating this group, on the other hand.
The number of rewriting rules depends on the extent of the description mechanism to be used and forming the basis of the parser. The description mechanism is in turn determined by the syntax and morpholygy of the language which imposes limitations on the parser in respect of its ability to arrive at a solution to the parsing in the event of a non-grammatical input. Only by including a very large number of rewriting rules in the parser is it possible to parse incorrectly composed and infrequently used sentence constructions. This in turn has the adverse effect of requiring a great deal of memory space for the rewriting rules in the computer on which the parser runs, and, at the same time requiring much longer time to parse such a sentence. In addition, under such conditions it is very difficult to detect nongrammatical expressions. Accordingly, it is the object of the invention to obviate these disadvantages and to provide a sentence processing method and means which detects a high number of nongrammatical expressions.